<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8">
    <title>8 模板语法-指令</title>
    <script src="js/vue.global.js"></script>
</head>
<body>
<div id = "app">
    <p style = "font-size:25px;">计数器: {{ counter }}</p>
    <button @click = "counter++" style = "font-size:25px;">点我</button>
</div>

<script>
    const app = {
        data() {
            return {
                counter: 1
            }
        }
    }
    vm = Vue.createApp(app).mount('#app')
    vm.$watch('counter', function(nval, oval) {
        alert('计数器值的变化 :' + oval + ' 变为 ' + nval + '!');
    });
</script>
</body>
</html>